Chip scale marker and method of calibrating marking position

ABSTRACT

A chip scale marker including a laser system, a wafer holder supporting a wafer to be processed, and a camera moving above the wafer holder by being connected to an X-Y stage and monitoring the wafer supported on a center hole of the wafer holder, the chip scale marker includes a unit detachably arranged on a laser beam path from the laser system and reducing power density of a laser beam, and a screen arranged on a center hole of the wafer holder and indicating a position where a laser beam from the laser system is irradiated.

BACKGROUND OF THE INVENTION

[0001] This application claims the priority of Korean Patent ApplicationNo. 2002-83202 filed Dec. 24, 2002 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to an apparatus and method ofcalibrating the marking position of a chip scale marker, and moreparticularly, to an apparatus and method of calibrating the markingposition of a chip scale marker which marks a character on a wafer chipusing a laser beam.

[0004] 2. Description of the Related Art

[0005] Several thousands or tens of thousands of chips are formed on awafer used in a semiconductor process. To classify the chips accordingto production lots, characters and/or numbers are marked on a surface ofeach chip. A chip scale marker using a laser beam is used as anequipment for marking.

[0006]FIG. 1 is a view illustrating a constitution of a typical chipscale marker. FIG. 2 is a view illustrating a constitution of the lasersystem of FIG. 1.

[0007] Referring to FIGS. 1 and 2, a wafer w is placed on a wafer holder20 and a laser system 30 is arranged under the wafer holder 20. A laserbeam oscillated by a laser oscillator 31 of the laser system 30 ismagnified by a beam expander 32 and input to a Galvano scanner 33. Thelaser beam input to the Galvano scanner 33 is irradiated onto chips onthe wafer w through an f-θ lens 34 so that characters are recorded on asurface of the chips. The above laser system is disclosed in JapanesePatent Publication No. H9-248692.

[0008] A camera 40 monitoring the wafer w being supported by the waferholder 20 is arranged above the wafer holder 20. The camera 40 is movedby being connected to an X-Y stage 50.

[0009]FIG. 3 is a view illustrating that a marking shape is distorted bythe Galvano scanner. The Galvano scanner 33 includes an x mirror 33 aand a y mirror 33 b. The x mirror 33 a controls movement of a laser beamin a direction x by an x drive (not shown) rotating a shaft 33 c at oneend of the x mirror 33 a. The y mirror 33 b controls movement of a laserbeam output from the x mirror 33 a in a direction y by a y drive (notshown) rotating a shaft 33 d at one end of the y mirror 33 b. Thus, anoptical path in the direction x is longer than that in the direction y.Accordingly, when a signal to mark a rectangular shape as shown in FIG.4A is transmitted, a distortion like a pin cushion as shown in FIG. 4Bis generated. Also, a positional error is generated due to a tinydifference in position between center lines of rotation shafts 33 c and33 d of the x and y mirrors 33 a and 33 b and surfaces of the x and ymirrors 33 a and 33 b.

[0010] In the meantime, as the beam having passed through the Galvanoscanner 33 passes through the f-θ lens 34, the beam is curved so that abarrel distortion is generated. To improve the distortion phenomenon ofthe marking, marking calibration should be periodically performed tocontrol the rotation of the x and y mirrors 33 a and 33 b of the Galvanoscanner 33.

[0011]FIG. 5 is a view illustrating a conventional method of measuring amarking error. According to the conventional method, a laser beam isirradiated onto a plate 70 having a shape and size corresponding to awafer and a plurality of small holes 70 a having a diameter of 0.3 mmformed in the plate 70 at a predetermined interval, and the position ofthe laser beam passing through each of the holes 70 a is observed by thecamera 40 and compared with a target position of the laser beam. Next, adegree of an error in the irradiation position of a laser beam isrecognized and a path along which the laser beam is irradiated iscorrected.

[0012] However, in the conventional method, since the laser beam passingthrough the holes 70 a is observed through a glass portion 42 in frontof the camera 40, a laser beam inclined with respect to the holes 70 a,as indicated by a dotted line of FIG. 5, is refracted by the glassportion 42 of the camera 40. Thus, an accurate position on the plate 70where the laser beam is irradiated is difficult to recognize and ittakes some time for the camera 40 to move above the holes 70 a to bemeasured. Also, the plate 70 may be damaged by power of the laser beam.

SUMMARY OF THE INVENTION

[0013] To solve the above and/or other problems, the present inventionprovides an apparatus and method of calibrating the marking position ofchip scale marker by radiating a laser beam onto a screen correspondingto a wafer by reducing power density of the laser beam in use by using apinhole apparatus and measuring the irradiated laser beam.

[0014] According to an aspect of the present invention, a chip scalemarker including a laser system, a wafer holder supporting a wafer to beprocessed, and a camera moving above the wafer holder by being connectedto an X-Y stage and monitoring the wafer supported on a center hole ofthe wafer holder, the chip scale marker comprising a unit detachablyarranged on a laser beam path from the laser system and reducing powerdensity of a laser beam; and a screen arranged on a center hole of thewafer holder and indicating a position where a laser beam from the lasersystem is irradiated.

[0015] The laser beam power density reducing unit is a pinhole apparatushaving a pinhole having a predetermined diameter.

[0016] The chip scale marker further comprises an ND filter reducing thequantity of the laser beam at a predetermined rate.

[0017] The pinhole apparatus is manufactured of invar or diamond. Thepinhole apparatus has a convex surface in a direction in which the laserbeam is input. In the pinhole apparatus, the diameter of the pinholeincreases along the laser beam path.

[0018] The screen comprises a lower layer absorbing the irradiated laserbeam and an upper layer transmitting the light from the lower layerupward in a vertical direction.

[0019] The screen comprises a lower layer made of glass or acryl whosesurfaces are roughly processed to disperse light at a point where thelaser beam is irradiated and an optical attenuator arranged above thelower layer to provide a single point upward by filtering the dispersedlight.

[0020] The screen is a semi-transmissive glass or paper.

[0021] The wafer holder further comprises a plurality of holes formed ona concentric circle separated a predetermined distance from the centerhole of the wafer holder and a semi-transmissive film provided on theholes.

[0022] A chip scale marker including a laser system, a wafer holdersupporting a wafer to be processed, and a camera moving above the waferholder by being connected to an X-Y stage and monitoring the wafersupported on the wafer holder, the chip scale marker comprising a unitdetachably arranged on a laser beam path from the laser system andreducing power density of a laser beam; a camera screen arranged infront of the camera; and a unit installing and removing the camerascreen at and from a front side of the camera.

[0023] The camera screen installing and removing unit is a unit rotatingthe camera screen.

[0024] The camera screen is a paper roller supported by two supportshafts so that, as a first support shaft rotates, paper wound around asecond support shaft is released to be wound around the first supportshaft.

[0025] The camera screen installing and removing unit reciprocates thecamera screen in a direction along the support shafts.

[0026] According to another aspect of the present invention, a method ofcalibrating a marking position of a chip scale marker including a lasersystem, a wafer holder supporting a wafer to be processed, a cameramoving above the wafer holder by being connected to an X-Y stage andmonitoring the wafer supported on the wafer holder, a unit detachablyarranged on a laser beam path from the laser system and reducing powerdensity of a laser beam, and a screen arranged on a center hole of thewafer holder and indicating a position where a laser beam from the lasersystem is irradiated, the method comprising the steps of radiating alaser beam using the laser system to a target position on the screen;measuring a position of the laser beam irradiated to the screen; andcalibrating the laser system by comparing the measured position of thelaser beam and a target position, wherein the screen is made of paper,and the position of the laser beam is a position where the screen ischanged black by the laser beam irradiated by the laser system whosepower density is reduced by the laser beam power density reducing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other features and advantages of the presentinvention will become more apparent by describing in detail preferredembodiments thereof with reference to the attached drawings in which:

[0028]FIG. 1 is a view illustrating a constitution of a typical chipscale marker;

[0029]FIG. 2 is a view illustrating a constitution of the laser systemof FIG. 1;

[0030]FIG. 3 is a view illustrating that a marking shape is distorted bythe Galvano scanner;

[0031]FIGS. 4A and 4B are views illustrating a pin cushion distortionphenomenon;

[0032]FIG. 5 is a view illustrating a conventional method of measuring amarking error.

[0033]FIG. 6 is a view illustrating a chip scale marker according to afirst preferred embodiment of the present invention;

[0034]FIG. 7 is a view illustrating a constitution of the laser systemof FIG. 6;

[0035]FIG. 8 is a view illustrating the pinhole apparatus of FIG. 6;

[0036]FIG. 9 is a sectional view illustrating a pinhole block of FIG. 8;

[0037]FIG. 10 is a view illustrating an optical path of a laser beamwhich is irradiated onto a screen;

[0038]FIG. 11 is a perspective view illustrating the wafer holder ofFIG. 6;

[0039]FIG. 12 is a view illustrating a center point of the camera and alaser beam point deviated therefrom;

[0040]FIG. 13 is a partially cut-away perspective view illustrating amodified example of the screen;

[0041]FIG. 14 is a view illustrating a chip scale marker according to asecond preferred embodiment of the present invention; and

[0042]FIG. 15 is a perspective view illustrating a modified example ofthe paper screen.

DETAILED DESCRIPTION OF THE INVENTION

[0043] A chip scale marker according to a first preferred embodiment ofthe present invention will now be described with reference to theaccompanying drawings. In the drawings, thicknesses of layers or areasshown in the drawings are exaggerated for the convenience ofexplanation.

[0044]FIG. 6 is a view illustrating a chip scale marker according to afirst preferred embodiment of the present invention. FIG. 7 is a viewshowing a constitution of the laser system of FIG. 6.

[0045] Referring to FIGS. 6 and 7, a screen 180 is placed on a waferholder and a laser system 130 is arranged under the wafer holder 120. Alaser beam oscillated by a laser oscillator 131 of the laser system 130is magnified by a beam expander 132 and input to a pinhole apparatus200. Of the laser beam input to the pinhole apparatus 200, only a laserbeam corresponding to a diameter of a pinhole 210 a passes through thepinhole 210 a to be diffracted. The diffracted laser beam passes througha Galvano scanner 133 and an f-θ lens 134 and is irradiated onto thescreen 180. The pinhole apparatus 200 limits a diameter through whichthe laser beam passes and diffracts the laser beam having passed thepinhole 210 a so that power density of a laser beam irradiated to atarget point is reduced.

[0046]FIG. 8 shows a constitution of the pinhole apparatus of FIG. 6.FIG. 9 is a sectional view illustrating a pinhole block of the pinholeapparatus of FIG. 8. A pinhole block 210 where the pinhole 210 a havinga predetermined diameter is formed is disposed at the center of thepinhole apparatus 200. A pinhole frame 220 separated a predetermineddistance from the pinhole block 210 is disposed around the pinhole block210. The pinhole lock 210 is elastically biased by springs 230 a and 230b in vertical and horizontal directions in the pinhole frame 220.Adjustment screws 240 a and 240 b supporting the pinhole block 210 areinstalled opposite to the springs 230 a and 230 b, respectively. Thescrews 240 a and 240 b adjust the position of the pinhole block 210 inthe pinhole frame 220 in the vertical and horizontal directions so thata proceeding axis of a laser beam is aligned to the pinhole 210 a. Thepinhole apparatus 200 is preferably configured such that it is attachedon a laser beam path during calibrating a marking position and detachedfrom the laser beam path during wafer marking by an attaching anddetaching means.

[0047] Equation 1 represents the strength of a laser beam passingthrough the pinhole 210 a. It can be seen that, as the diameter of thepinhole 210 a decreases, the strength of the laser beam passing throughthe pinhole 210 a decreases. $\begin{matrix}{{P(r)} = {{P(\infty)} \times \left\lbrack {1 - {\exp\left( {{- 2} \times \frac{r^{2}}{R^{2}}} \right)}} \right\rbrack}} & \left\lbrack {{Equation}\quad 1} \right\rbrack\end{matrix}$

[0048] Here, “P(r)” denotes the strength of a laser beam passing throughthe pinhole 210 a, “P(∞)” denotes the strength of a laser beam incidenton the pinhole 210 a, “R” denotes the radius of a laser beam incident onthe pinhole 210 a, and “r” denotes the radius of the pinhole 210 a.

[0049] The pinhole apparatus 200 where the laser beam directly contactsis preferably manufactured of invar or diamond exhibiting less thermaldeformation. Preferably, one side of the pinhole apparatus 200 is formedconvex in a direction where the laser beam is input so that the laserbeam irradiated onto the pinhole apparatus 200 is reflected andscattered outwardly. This is to prevent the reflected laser beam fromproceeding back to the laser oscillating apparatus 131. Also, thediameter of the pinhole 210 a preferably increases along the path of thelaser beam to facilitate diffraction of the laser beam passing throughthe pinhole 210 a and reduce power density of the laser beam.

[0050] The Galvano scanner 133 includes an x mirror 133 a and a y mirror133 b. The x mirror 133 a controls movement of a laser beam in adirection x by using an x drive (not shown) rotating a shaft (not shown)at one end of the x mirror 133 a. The y drive (not shown) controlsmovement of a laser beam output from the x mirror 133 a in a directiony.

[0051] A camera 140 observing the wafer or the screen 180 is installedabove the wafer holder 120. The camera 140 is supported and moved by anX-Y stage 150. The camera 140 and the X-Y stage 150 transmit anelectrical signal to a controller 170. The controller 170 controls theGalvano scanner 133 and the X-Y stage 150.

[0052] The screen 180 has the same shape and size as those of the waferto be marked and is formed of two layers as shown in FIG. 10. A lowerlayer 182 is a fluorescent layer which illuminates by absorbing a laserbeam while an upper layer 184 is a layer which transmits the laser beampassing through the fluorescent layer. The lower layer 182 is placed ata center hole 122 of FIG. 11 of the wafer holder and preferably rigid toa degree so as not to be deformed.

[0053]FIG. 11 is a perspective view illustrating the wafer holder ofFIG. 6. A plurality of holes 124 are formed around the center hole 122where the wafer is accommodated. A semi-transmissive film 126semi-transmitting light is attached on the holes 124. The holes 124 arepreferably arranged coaxially outside a center shaft of the center hole122. The semi-transmissive film 126 has the same function as the screen180.

[0054] The operation of the chip scale marker 100 having the aboveconstitution is described below with reference to the accompanyingdrawings.

[0055]FIG. 10 is a view illustrating an optical path of a laser beamwhich is irradiated onto the screen 180. FIG. 12 is a view illustratinga center point of the camera and a laser beam point deviated therefrom.

[0056] The screen 180 instead of the wafer is disposed on the waferholder 120. When a laser beam is oscillated by the laser oscillator 131,the laser beam passes through the beam expander 132, the pinholeapparatus 200, the Galvano scanner 133, and the f-θ lens 134 to beirradiated onto a target position of the screen 180. The irradiatedlaser beam is absorbed by the lower layer 182 that is a fluorescentlayer and a light emitted therefrom form a laser beam point 148 at thelower layer 182 and proceeds upward after passing through the upperlayer 184 that is a transmittance layer. At this time, the lightincident on the screen 180 to be inclined (the laser beam indicated byan imagery line of FIG. 10 proceeds vertically with respect to thecamera 140 disposed thereabove along an optical path indicated by adotted line in FIG. 10. The laser preferably used a Nd:YAG laser and avisible ray which is a green light having a 532 nm wavelength that is asecond harmonic wave. Also, the camera 140 preferably uses a vision CCDcamera capable of recognizing the laser beam in use.

[0057] The camera 140 which is moved by the X-Y stage 150 to be disposedabove a target point 146 of the laser beam reads the laser beam point148 formed on the screen 180 under the camera 140. The camera 140recognizes a deviation of the beam point 148 from the center point 146of the camera 140 and inputs the X-Y coordinate of the deviation to thecontroller 170. The beam point confirmation process is performed byrepeating the above-described step at a plurality of positionscorresponding to the positions of the chips.

[0058] The controller 170 analyzes the input positional information andcontrols the mirrors of the Galvano scanner 132 so that a light beam isirradiated on the position of a wafer chip. Next, after the screen 180is removed, the wafer is installed on the wafer holder 120. The positionwhere the wafer is installed is the same as the position where thescreen 180 is placed. The laser beam oscillated by the laser 130 isirradiated to a corrected position on the wafer to perform marking.

[0059] When a movement of the Galvano scanner 132 during laser markingis to be detected, a laser beam is irradiated on the semi-transmissivefilm 126 on the hole 124 of the wafer holder 120 and the camera 140 ismoved upward from the target point where the laser beam is to beirradiated so that a beam point irradiated in the above-described methodis detected and the laser beam is calibrated.

[0060] In the above preferred embodiment, the pinhole apparatus 200which is detachable is used to reduce the power density of the laserbeam. However, a neutral density filter (ND filter) having lighttransmittance of 10-50%, for example, is used instead of the pinholeapparatus 200, or the pinhole apparatus 200 and the ND filter can beused together.

[0061] In a modification of the screen, glass or acryl where a surfaceto which a laser beam is irradiated is roughly processed is arranged atthe lower layer and an optical attenuator is arranged above the glass oracryl. When a laser beam is irradiated on the screen, the laser beam isdispersed on the roughly processed surface of the lower layer. The laserbeam irradiated at an angle is dispersed so as not to be transmitted inan inclined direction. The irradiated laser beam forms an image on thelower layer. The optical attenuator classifies the point to which thelaser beam is irradiated among the dispersed light in the lower layer.Since the light passing through the optical attenuator displays one beampoint, the beam point can be easily observed by using the camera 140.

[0062]FIG. 13 shows a screen according to another preferred embodimentof the present invention. A semi-transmissive sheet 284 is attached to acircular frame 282 having the same size as the wafer. For example, asemi-transmissive paper, can be used for the semi-transmissive sheet284. The semi-transmissive sheet 284 displays a point made by a colorlaser beam to indicate the position of the laser beam. Also, although atwo-layered screen is used in the above-described preferred embodiment,when a hard and semi-transmissive material like semi-transmissive glassis to be used, a one-layer screen can be used.

[0063] In the above preferred embodiment, the beam point of the screenis measured with the CCD camera by using a laser beam having thewavelength of a visible ray. When a laser beam having the wavelength ofan infrared ray or an ultraviolet ray, not the wavelength of a visibleray, a paper screen is used as the screen to detect the beam where thelaser beam is irradiated. The beam point of the screen is changed blackby slightly burning with properly lowered power density of the laserbeam irradiated to the screen. The above method using the paper screencan be applied to a marking calibrating system using a laser beam havingthe wavelength of a visible ray.

[0064]FIG. 14 shows a marking position calibrating apparatus of a chipscale marker 300 according to a second preferred embodiment of thepresent invention. Here, the same constituent elements have the samereference numerals as those of the first preferred embodiment anddetailed descriptions thereof will be omitted.

[0065] Referring to FIG. 14, a motor 392 to install and remove a camerascreen 390 in front of the camera 140 is arranged on a support rod 142supporting the camera 140. In FIG. 14, a case in which the camera screen390 is installed in front of the camera 140 is indicated by a solid linewhile a case in which the camera screen 390 is removed from the frontside of the camera 140 is indicated by a dotted line. The camera screen390 is preferably arranged close to a wafer holder 320. A center hole322 is formed at the center of the wafer holder 320 and a laser beam isirradiated from the laser system 130 through the center hole 322 to thecamera screen 390. Any type of the screen applied to the above preferredembodiments can be applied to the camera screen 390.

[0066] When a marking position is to be detected by using the screen390, the camera screen 390 is arranged in front of the camera 140 bydriving a motor 392. Next, the camera 140 and the camera screen 390 aremoved to predetermined positions by using the X-Y stage 150 tocorrespond to the position of the wafer where the laser beam isirradiated and the laser beam is irradiated to the camera screen 390.Then, a beam point formed on the camera screen 390 is observed by thecamera 140 and the positional information of the beam point is input tothe controller 170.

[0067]FIG. 15 is a perspective view illustrating an example of using apaper screen by installing the same in front of the camera. Referring toFIG. 15, a paper roller 401 used as a paper screen is supported by beingwound around first and second support shafts 402 and 403 and separated apredetermined distance from the camera 440. A horizontal surface of thepaper roller 401 to which a laser beam is irradiated is preferablyarranged close to the marking surface of the wafer loaded on the waferholder. As the first support shaft 402 is rotated, paper wound aroundthe second shaft 403 is released and wound around the first supportshaft 402. The first and second support shafts 402 and 403 are installedat the camera 440 via a connection member 404 to be capable of slidingin a direction perpendicular to a direction in which the paper issupplied, which is indicated by an arrow A. A guide member 406 guidingsliding of the connection member 404 with respect to the camera 440 isarranged between the camera 440 and the connection member 404. Referencenumeral 407 is a portion extending from the connection member 404 towardthe inner side of the paper roller 401 so that the marking surface ofthe paper screen makes a plane perpendicular to the direction of thelaser beam of the laser system 130.

[0068] During calibration of the marking position of the chip scalemarker, the connection member 404 including the paper roller 401 ismoved above the wafer holder along the guide member 406 so that thecamera 440 including the paper roller 401 performs a marking job. Whilethe connection member 404 is moved in a direction indicated by an arrowB, the paper roller 401 is located at a position where a field of viewof the camera exists. The paper roller 401, that is, a paper screen, islocated in the field of view of the camera as being moved along n the Xaxis while wound around the first support shaft 402 and the position onthe Y axis is adjusted along the guide member 406. Next, a laser beam isirradiated onto the paper screen in the above method to change the paperscreen black. Then, the camera 440 measures the black point to calculatedeviation from a target point.

[0069] As described above, according to the chip scale marker and methodof calibrating a marking position according to the present invention,the direction of laser beam can be calibrated by measuring the positionmarked on a wafer chip before wafer marking. Also, during marking, asimple adjustment of a laser beam can be made by radiating a laser beamto a semi-transmissive film formed at the edge of the wafer holder andmeasuring a point of the laser beam. Furthermore, since calibration isperformed with respect to the laser beam point on the screen, thecalibration is accurate so that marking can be made at an accurateposition on the wafer chip. The method of calibrating a marking positionwhich checks the marking position by changing the paper screen black canbe applied to a chip scale marker using the wavelength of an ultravioletray or an infrared ray in addition to a chip scale marker using thewavelength of a visible ray.

[0070] While this invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A chip scale marker including a laser system, awafer holder supporting a wafer to be processed, and a camera movingabove the wafer holder by being connected to an X-Y stage and monitoringthe wafer supported on a center hole of the wafer holder, the chip scalemarker comprising: a unit detachably arranged on a laser beam path fromthe laser system and reducing power density of a laser beam; and ascreen arranged on a center hole of the wafer holder and indicating aposition where a laser beam from the laser system is irradiated.
 2. Thechip scale marker as claimed in claim 1, wherein the laser beam powerdensity reducing unit is a pinhole apparatus having a pinhole having apredetermined diameter.
 3. The chip scale marker as claimed in claim 2,further comprising an ND filter reducing the quantity of the laser beamat a predetermined rate.
 4. The chip scale marker as claimed in claim 1,wherein the laser beam power density reducing unit is an ND filter whichreduces the quantity of the laser beam at a predetermined rate.
 5. Thechip scale marker as claimed in claim 2, wherein the pinhole apparatusis manufactured of invar or diamond.
 6. The chip scale marker as claimedin claim 2, wherein the pinhole apparatus has a convex surface in adirection in which the laser beam is input.
 7. The chip scale marker asclaimed in claim 6, wherein, in the pinhole apparatus, the diameter ofthe pinhole increases along the laser beam path.
 8. The chip scalemarker as claimed in claim 1, wherein the screen comprises: a lowerlayer absorbing the irradiated laser beam; and an upper layertransmitting the light from the lower layer upward in a verticaldirection.
 9. The chip scale marker as claimed in claim 1, wherein thescreen comprises: a lower layer made of glass or acryl whose surfacesare roughly processed to disperse light at a point where the laser beamis irradiated; and an optical attenuator arranged above the lower layerto provide a single point upward by filtering the dispersed light. 10.The chip scale marker as claimed in claim 1, wherein the screen is asemi-transmissive glass.
 11. The chip scale marker as claimed in claim1, wherein the screen is paper.
 12. The chip scale marker as claimed inclaim 1, wherein the wafer holder further comprises: a plurality ofholes formed on a concentric circle separated a predetermined distancefrom the center hole of the wafer holder; and a semi-transmissive filmprovided on the holes.
 13. A chip scale marker including a laser system,a wafer holder supporting a wafer to be processed, and a camera movingabove the wafer holder by being connected to an X-Y stage and monitoringthe wafer supported on the wafer holder, the chip scale markercomprising: a unit detachably arranged on a laser beam path from thelaser system and reducing power density of a laser beam; a camera screenarranged in front of the camera; and a unit installing and removing thecamera screen at and from a front side of the camera.
 14. The chip scalemarker as claimed in claim 13, wherein the camera screen installing andremoving unit is a unit rotating the camera screen.
 15. The chip scalemarker as claimed in claim 13, wherein the camera screen is paper. 16.The chip scale marker as claimed in claim 15, wherein the camera screenis a paper roller supported by two support shafts so that, as a firstsupport shaft rotates, paper wound around a second support shaft isreleased to be wound around the first support shaft.
 17. The chip scalemarker as claimed in claim 16, wherein the camera screen installing andremoving unit reciprocates the camera screen in a direction along thesupport shafts.
 18. A method of calibrating a marking position of a chipscale marker including a laser system, a wafer holder supporting a waferto be processed, a camera moving above the wafer holder by beingconnected to an X-Y stage and monitoring the wafer supported on thewafer holder, a unit detachably arranged on a laser beam path from thelaser system and reducing power density of a laser beam, and a screenarranged on a center hole of the wafer holder and indicating a positionwhere a laser beam from the laser system is irradiated, the methodcomprising the steps of: radiating a laser beam using the laser systemto a target position on the screen; measuring a position of the laserbeam irradiated to the screen; and calibrating the laser system bycomparing the measured position of the laser beam and a target position,wherein the screen is made of paper, and the position of the laser beamis a position where the screen is changed black by the laser beamirradiated by the laser system whose power density is reduced by thelaser beam power density reducing unit.
 19. The method as claimed inclaim 18, wherein the laser beam power density reducing unit is apinhole apparatus having a pinhole having a predetermined diameter. 20.The method as claimed in claim 19, wherein the laser beam power densityreducing unit further comprises an ND filter reducing the quantity ofthe laser beam at a predetermined rate.
 21. The method as claimed inclaim 18, wherein the laser beam power density reducing unit is an NDfilter which reduces the quantity of the laser beam at a predeterminedrate.